I like the idea of being able to keep them out of the sun and wind when traveling so a camper top is probably the best option for me. I'm not worried about them being unrestrained since the tops secure closed; I can always tie their leashes into the bed tie downs.

IMO... not good to just throw them in back or tie up on leash. You have to consider their safety. I would keep them in a secure kennel weather in back of truck or TT

I got a tailgate seal for mine and installed it today. It seals the gap between the bed and the tailgate. My last company truck would get filthy back inside the camper shell when I went down dirt roads and down the railroad tracks for miles. I literally had a quarter inch of dirt in it once... not a fun clean-out job...